Display screen or portion thereof with a transitional graphical user interface



7. Display screen or portion thereof with a transitional graphical user interface

7.1 : Front, first image in a sequence

7.2 : Front, second image in a sequence

7.3 : Front, third image in a sequence

The outer perimeters shown in broken lines in design 7 illustrate a display screen or portion thereof and form no part of the claimed design; the remaining broken lines in the figures illustrate portions of the graphical user interface that form no part of the claimed design; the appearance of the transitional image sequentially transitions between the images shown in reproductions 7.1 through 7.3 ; the process or period in which an image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 